Mastering Concepts 5 1 1 What is photosynthesis Describe the reactants and products in words and in chemical symbols Photosynthesis is the chemical process in which plants algae and some microorganisms convert solar energy into chemical energy A photosynthetic cell uses light energy to form glucose and oxygen gas from carbon dioxide and water The chemical equation is light energy 6CO2 6H2O C6H12O6 6O2 2 Why is photosynthesis essential to life on Earth Photosynthesis is essential to life on Earth because almost all life on the planet ultimately depends on it for a food source 3 What happens to the glucose that plants produce The glucose that plants produce in photosynthesis is used as fuel for the plant s own cellular respiration which generates the ATP that powers biochemical reactions and allows the plant to grow The glucose is also used to produce other chemical compounds including amino acids and to produce cellulose for plant cell walls Excess glucose is stored as starch or sucrose 4 How is an autotroph different from a heterotroph Autotrophs can make their own organic compounds but heterotrophs have to get their carbon by consuming other organic compounds 5 How did the origin of photosynthesis alter Earth s atmosphere and the evolution of life The evolution of photosynthesis filled the atmosphere with O2 gas giving an evolutionary advantage to those organisms that could use O2 in respiration to produce the most energy The oxygen also helped produce the ozone layer which decreased damage from the sun and lead to an explosion in life s diversity 5 2 1 What are the three main components of sunlight The three main components of sunlight are high energy radiation such as ultraviolet radiation visible light and low energy radiation such as infrared radiation 2 Describe the relationship among the chloroplast stroma grana and thylakoids Chloroplasts are organelles that contain the other structures or substances Inside the chloroplast the stroma is a fluid filled space that surrounds grana which are stacks of thylakoids 3 How does it benefit a photosynthetic organism to have more than one type of pigment Multiple pigments allow a photosynthetic organism to absorb energy from a broader range of wavelengths of light 4 How does the reaction center chlorophyll interact with the antenna pigments in a photosystem The antenna pigments capture light energy and send it to the reaction center chlorophyll which uses it for the reactions of photosynthesis 5 3 1 What happens in each of the two main stages of photosynthesis In the first stage of photosynthesis light reactions light energy is captured by pigments and converted to the chemical energy of ATP and NADPH In the second stage of photosynthesis carbon reactions the energy of ATP and the electrons in NADPH are used to make glucose from CO2 2 Where in the chloroplast do the light reactions and the carbon reactions occur The light reactions occur in the thylakoid membrane of a chloroplast and the carbon reactions occur in the stroma of a chloroplast 5 4 1 Describe the events in photosystem II beginning with light and ending with the production of ATP In photosystem II light strikes a photosynthetic pigment energy is absorbed energy bounces to the chlorophyll molecule in the reaction center which releases two energized electrons the electrons are replaced by two electrons stripped from a water molecule forming oxygen gas O2 and two hydrogen ions H as the energized electrons move along the proteins of the electron transport chain of photosystem II hydrogen ions build up in the space within the thylakoid forming a reservoir of potential energy as ATP synthase moves hydrogen ions back to the stroma the released energy bonds a phosphate group onto ADP forming ATP 2 How do electrons pass from photosystem II to photosystem I Electrons pass from photosystem II to photosystem I in the electron transport chain Light strikes antenna pigments in photosystem I these pigments transfer the energy to the reaction center chlorophyll molecule of photosystem I The reaction center chlorophyll releases two energized electrons which are replaced by the electrons from photosystem II 3 How are the electrons from photosystem II replaced The boosted electrons lost from the reaction center in photosystem II are replaced by electrons stripped from a water molecule 4 What happens in photosystem I In photosystem I energy from sunlight energizes a pair of electrons in the reaction center replaced by a pair of electrons from photosystem II and these are passed to molecules of NADP to reduce them to NADPH This molecule carries the electrons and potential energy to the carbon reactions of photosynthesis 5 5 1 What is the product of the carbon reactions The carbon reactions produce the three carbon molecule PGAL 2 What are the roles of rubisco RuBP ATP and NADPH in the Calvin cycle Rubisco is an enzyme used to fix CO2 by combining it with RuBP which is a five carbon sugar ATP provides the necessary energy and NADPH the necessary electrons for this reaction 3 What is the relationship between the light reactions and the carbon reactions The light reactions provide the energy and electrons for the carbon reactions in the form of ATP and NADPH The carbon reactions use the energy and electrons from the light reactions to reduce CO2 forming organic molecules such as glucose 5 6 1 Why is the Calvin cycle also called the C3 pathway The Calvin cycle is called the C3 pathway because the first stable compound produced is the three carbon molecule PGA 2 How does photorespiration counter photosynthesis In photorespiration the rubisco enzyme uses O2 instead of CO2 The resulting chemical reaction liberates CO2 that has already been fixed and thus counters photosynthesis 3 What conditions maximize photorespiration Photorespiration is more likely when plants close their stomata to minimize water loss letting CO2 levels fall while O2 levels rise 5 7 1 Describe how a C4 plant minimizes photorespiration The leaves of C4 plants have a distinctive arrangement of mesophyll cells and bundle sheath cells Each vein is surrounded by a concentric ring of bundle sheath cells that in turn are surrounded by a concentric ring of mesophyll cells In mesophyll cells CO2 is converted to a 4 carbon compound oxaloacetate which is reduced to malate The malate then moves to the bundle sheath cells where the CO2 is released to the Calvin cycle The high CO2 concentration and low O2 concentration in the bundle sheath